Magnetron amplifier



2 Sheets-Sheet 1 D. A. WILBUR EFAL MAGNETRON AMPLIFIER Fig/a.

May 22. 1956 Filed May 10, 1950 Inventors: Donald A.Wilbun PnH.PC1Y5,JY.

Their Attorney ANODE CUR RENT SOURCE OF DR! VING SIGNAL BUFFER AMPLIFIERy 22, 1956 D. A. WILBUR ETAL 2,747,031

MAGNETRON AMPLIFIER Filed May 10, 1950 2 Sheets-Sheet 2 y} l a! 44 3'2as 3 4/ 36 27 27 27 38 15 37 57 fi 2e 30 J0 Invent, ors: DonaidA.Wilbu1;

Philip lipebersflr, by WW4 KM Their" Attorney.

United States Patent MAGNETRON AMPLIFIER Donald A. Wilbur, Albany, andPhilip H. Peters, .lr., Schenectady, N. Y., assignors to GeneralElectric Company, a corporation of New York Application May 10, 1950,Serial No. 161,052

1 Claim. (Cl. 179-171) This invention relates in general to method andapparatus for amplifying electromagnetic signals, and in particularrelates to improvements in high frequency magnetron apparatus directedto the purpose of amplifying electromagnetic energy at the highfrequency end of the electromagnetic spectrum.

Magnetrons are extensively used as generators of high frequencyelectromagnetic energy. They are used for this purpose because they areadapted to the generation of large amounts of power at high efficienciesat the high frequency end of the electromagnetic spectrum. Heretofore,apparatus for amplifying high frequency electromagnetic energy has notapproached the power output and efiiciency capabilities of the magnetronapparatus functioning as a generator of high frequency electromagneticoscillations. Amplifying apparatus for delivering large amounts of powerat the high frequency end of the electromagnetic spectrum constitutes areal and pressing need in the art. Amplifying apparatus that can amplifyto high power levels and at high efficiencies is even more welcome inthe art.

Accordingly, it is an object of our invention to provide means foramplifying electromagnetic energy.

It is another object of our invention to provide a highly efficientamplifier of high frequency electromagnetic energy.

It is a further object of our invention to provide magnetron apparatusfor amplifying high frequency signals to high power levels.

In an exemplary embodiment of the invention, shown in the drawings,magnetron apparatus is adapted for the purpose of amplifyingelectromagnetic energy by providing means for coupling energy into themagnetron apparatus and operating the magnetron in a manner so thatenergy is developed only When signals to be amplified are coupled intothe magnetron apparatus.

The features of the invention desired to be protected herein are pointedout in the appended claims. The invention itself together with itsfurther objects and advantages may best be understood by reference tothe following description taken in connection with the accompanyingdrawing in which Fig. 1:: shows a schematic representation of amagnetron useful in explaining the operation of the invention; Fig. lbshows a schematic diagram of a circuit useful in explaining theoperation of the invention; Fig. 2 is a simplified anode voltage vs.anode current characteristic of a typical magnetron of the kind underdiscussion in this specification; Fig. 3 is a semischematicrepresentation of apparatus by means of which the invention may becarried out; Fig. 4 shows diagrammatically another embodiment by meansof which the invention may be carried out; Figs. 5a and 5b show theconstructional details of the composite magnetron devices of the kindthat may be used in the apparatus of Figs. 3 and 4 in carrying out theinvention; Fig. 50 being a plan view and Fig. 5b being a side view.

A typical magnetron generator of electromagnetic oscillations comp-risesa cylindrical anode structure with resonant cavities symmetricallylocated around the periphery of the inner cylindrical surface of theanode, and a cathode located axially within the generally cylindricalchamber defined by the cylindrical anode structure. When aunidirectional magnetic field of proper magnitude and a unidirectionalelectric field of proper magnitude are applied to the aforementionedstructure in a manner well known in the art, the magnetron developsuseful high frequency electromagnetic energy.

Referring now to Fig. In, there is shown a developed view of a travelingwave type of magnetron such as was briefly described in the paragraphabove. This view shows a series of anode segments, collectivelydesignated by numeral in, and a cathode 2. Resonators or resonantcircuits, collectively designated by the numeral 3, are connectedbetween the anode segments 1a as shown. Of course, the space between theanode segments 1a and the cathode 2 is evacuated. By adjusting the axialmagnetic field, symbolically designated by H, and the unidirectionalelectric field between the anode and cathode symbolically designated byE, to a value such that the average drift velocity of the electrons inthe space between the anode and cathode corresponds to the frequency towhich resonators 3 are tuned, the magnetron can be made to convertenergy from the unidirectional power source supplying the electric fieldinto useful high frequency electromagnetic energy.

The explanation of the manner in which the foregoing conversion ofenergy is effected is complicated; however. a simplified explanation maybe advanced to give an appreciation of the nature of the effectsinvolved. The high frequency electromagnetic fields existing in theresonators extend out and fringe the anode segments as schematicallyindicated by E. In the steady state operation these fields cause themoving electron space charge to assume a spoke shaped form, the numberof spokes depending on the number of anode segment interaction gaps.When the spokes of space charge impelled by the unidirectional forcesfrom the unidirectional magnetic and electric fields exerted on theelectron space charge move against the high frequency fringing field Eenergy is developed in the resonators 3. It should be noted that theaverage drift velocity of the electrons should-correspond to theresonant frequency of the resonators connected to the anode segments.When the average drift velocity of the electrons corresponds to theresonant frequency of the resonators, the electron space charge is thensaid to be in synchronism. If the average drift velocity is less thanthis value there is no net interchange of energy from the elec trons tothe high frequency fields associated with the resonator. The averagedrift velocity of the electrons is dependent upon the ratio E/H, where Eis the electric field intensity and H is the magnetic field intensity ofthe unidirectional fields within the space charge chainber. Thus, if thevalue of unidirectional voltage between the anode segments and thecathode is reduced to such an extent that the average drift velocity ofelectrons is less than the value of drift velocity which corresponds tothe frequency to which the resonators are tuned, then no high frequencyenergy will be developed in the resonators. It will be understood thatthe foregoing planation applies in particular to the operation of atravcling wave magnetron as an oscillator as distinct from magnetronoperation at cyclotron frequency. It should be understood that since theabove description applies to Fig. 1a which is a developed view of acylindrically shaped magnetron, the term average angular velocity willbe the appropriate expression to use in connection with the actualstructure.

In Fig. 2 is shown, somewhat simplified, the unidirectional anodevoltage versus the unidirectional anode current characteristics of atypical magnetron of the kind under discussion herein. V represents themagnitude of voltage applied between the anode segments 1a and thecathode 2. I represents the magnitude of the unidirectional currentflowing between the cathode and anode or, in other words, the currentsupplied by the unidirectional power source. The voltage source Vproduces the electric field E. From Fig. 2 it can be seen generally themanner in which the voltage and current in a magnetron of the kindschematically shown in Fig. 1a varies. As the anode voltage is increasedfrom zero magnitude the anode current increases without any energy beingdeveloped in the resonators. This is usually referred to as leakagecurrent. A point 4 is eventually reached as the voltage is increased atwhich oscillations in the resonators start, and as the voltage isincreased the amount of power developed in the resonators increases. Asthe voltage is raised it should be kept in mind that the E factor of theratio E/H is changed to bring the angular velocity of the electrons upto the oscillation point. Below this point the E/H ratio was less thanthat required to sustain oscillations. Assume for the moment that thevoltage applied to the magnetron the magnetic field of course beingconstant, corresponds to the value of point 5, that is, the voltageapplied has a value below the oscillation point 4. This voltage may beapplied, for example, by means of a fixed battery. Let a second batterybe connected in series with the first battery so that the total appliedunidirectional voltage corresponds to the value of point 6, the secondbattery contributing the increment of anode voltage delta V. It isreadily appreciated from the foregoing discussion that this magnitude ofvoltage on the magnetron along with the effects of the high frequencyvoltages produced in the magnetron is sufficient to raise the E/H ratioto a value at which the average anuglar velocity of the electronscorresponds to the resonant frequency of the resonator. Oscillations aredeveloped in the resonator in accordance with the preceding explanationand energy is converted from the unidirectional source into the highfrequency field associated with the resonators. At this latter value thepower supplied to the magnetron is measured by the product of (V+AV) I.The first battery contributes the magnitude of power represented by V Iand the magnitude of power contributed by the second battery isrepresented by AVXI. The high frequency energy developed by themagnetron is (V+AV) XIx an efliciency factor. It should be noted thatthe magnitude of the power contributed by the second battery is muchsmaller than the total high frequency power delivered by the magnetron.This latter fact may readily be appreciated from the following numericalexample. Assume that a magnetron develops high frequency power with ananode voltage of 1000 and draws anode current of 2 amperes. Assumefurther that this magnetron operates at an efficiency of 50%. The highfrequency power output will be 1000 watts (1000 2 .50). Assume furtherthat the second battery contributes 50 volts of the anode voltage. Thepower input into the magnetron of the second battery will be 100 watts(50x2). This indicates that by supplying an incremental energy of 100watts to the magnetron, 1000 watts of high frequency energy can beobtained from the magnetron. The applicants have found that theincremental energy supplied by an external source of energy can be ahigh frequency source; and hence with reference to the example underconsidera tion by supplying 100 watts of high frequency energy, 1000watts of high frequency energy can be obtained from the magnetron, thatis, amplification of high frequency energy is achieved with a poweramplification of 10. It should be understood that the above numericalcalculations are given by way of example to facilitate understanding ofthe principle involved.

- In Fig. 1b there is shown a schematic representation of a split anodemagnetron in which a batterysupplies the electrical field between thecathode 2 and anode 1b. While in the preceding description, for thepurpose of simplicity of explanation, a second battery has been added toincrease the electric field between anode and cathode, the highfrequency energy is not supplied to the magnetron in this way, that is,it is not supplied in series between the cathode and anode, but ratherit is supplied in series between the anodes as diagrammaticallyindicated by the arrow. The increment of high frequency voltage suppliedbetween anode segments is designated AV in Fig. 1b. With the highfrequency energy introduced in this manner, the electrical field inone-half of the split anode magnetron is alternately augmented as thehigh frequency energy passes through its periodic time variations; theeffect is substantially the same as supplying the electrical field bymeans of a battery placed in series between the cathode and the anodes.The use of high frequency energy to supply the component of the electricfield necessaryto raise the electric field to a value that will causethe magnetron to develop useful power does not in principle differ fromthe use of a battery for this purpose.

With reference to Fig. 2 is should be noted that the first battery maysupply a value of potential varying between 0 and the value V and thatthe value V need not be a value just below the operating point 4.- Ifthe point 5, corresponding to the potential suppliedby the first batteryis appreciably below point 4, then an appreciable amount of input energymust be supplied before the magnetron starts amplifying. If thepotential supplied by the first battery corresponds to point 4, then ofcourse very little, if any, input energy need be supplied before themagnetron starts amplifying. If the potential supplied by the firstbattery is above the point 4, the magnetron will be in an oscillatingcondition when a signal is applied, yet the magnetron will stillfunction to amplify the signal supplied. It has been found that even ifa potential corresponding to the upper current cutoff potential of themagnetron is applied and the magnetron is delivering the maximum powerit is capable of delivering as an oscillator, that additional power maybe obtained from the magnetron by supplying high frequency energy to themagnetron and causing it to func tion as an amplifier. Even at the uppercurrent cutofi point the magnetron will amplify high frequency energyinput in proportion to the input.

It will be understood that for the sake of simplicity of explanation theabove remarks apply to a magnetron operated in a particular mode, thear-mode for instance. Assuming that the plot of Fig. 2 relates to amagnetron operating in the Ir-IIlOdE, it should be noted that at somevalue between 0 and V, other than at point 5, the magnetron may operateas an oscillator on some other mode besides the ar-mode. Of course, thiscondition should be avoided in selecting the operating point 5.

While in Fig. l resonators are shown connected by the anode segments, itwill be understood that in general this figure describes an oscillator.It should be noted that in applicants magnetron amplifier a resonatorneed not be used but that any suitable high impedance may be used inplace of a resonator. Further, in the case of an oscillator a resonantcircuit establishes the frequency of oscillation in the magnetron.amplier the frequency is pre-determined by the frequency of the inputsignal. If a resonator is used to obtain a high impedance, then ofcourse, the input signal should correspond to the resonant frequency ofthe resonator;

The exemplary embodiments shown and described in fication to high powerlevels of high frequency electro-l magnetic energy.

Referring now to Fig. 3 there is shown apparatus for carrying out theinvention comprising a parallel wire type of traveling wave magnetronadapted to amplify electro-' In the case of the magnetron magneticenergy, and a source of signal to be amplified which is connected to themagnetron through a buffer amplifier. The parallel wire type ofmagnetron shown in this figure is used by way of illustration and itshould be understood that generally any of the other types of travelingwave type of magnetrons including those having more than two anodesegments may be utilized as amplifiers in applicants system. The bufferamplifier also may be eliminated and is included for the purpose ofisolating the source of signal from the magnetron amplifier proper.

Referring now to the particularities of construction of the magnetron inthis figure, there is shown a parallel wire transmission line 7short-circuited at one end by the fixed connection 8 and at the otherend by a movable connection 9 which is utilized for the purpose oftuning the resonant line 7. Intermediate the ends of this section oftransmission line is connected a load 10 which may be adapted toslidably move along the transmission line 7. It should be understoodthat the load 10 may represent other apparatus to which power iscoupled. It should further be understood that the load may have asubstantial reactive component without disturbing the basic operation ofthe amplifier. Near the end of the transmission line 7 with the fixedshort-circuited connection 8 are located a pair of anode blocks 11 and12 connected to the transmission line. On their inward sides anodeblocks 11 and 12 are shaped to form a generally cylindrical opening inwhich a cathode 13 is axially located as shown in the figure. Battery 14is shown for energizing the cathode and a second battery 15 is shown forenergizing the anodes 11 and 12. This source is connected, as is readilyseen from the drawing, between the anode blocks 11 and 12 and thecathode 13. A unidirectional magnetic field is supplied by any of avariety of means schematically indicated by a coil 16 in the drawing. Aslidable tap 17 is connected to a point on the transmission line 7intermediate the short-circuited ends to couple electromagnetic energyinto the resonant system. Preferably, tap 17 is adjusted in such amanner that there is a maximum power transfer from a buffer amplifier 18to the resonator system. The driving signal, that is the signal to beamplified, is supplied to the magnetron apparatus through bufferamplifier 18 and through a section of coaxial transmission line 17aconnecting the buffer amplifier to the magnetron. Various other ways ofcoupling power from the source of signal to be amplified into themagnetron amplifier may be used other than the direct sliding connectionas shown. For instance, various well known inductive and capacitivecoupling means may be used.

In utilizing the apparatus of Fig. 3 to amplify electromagnetic energy,cathode 13 of the magnetron is heated by means of battery 14 and theresonant frequency of the system is adjusted by means of tuner 9 topresent a high impedance at the anode blocks at the frequency of thesignal to be amplified. Anodes 11 and 12 are so energized that the ratioof the electric field intensity between the cathode and the anode to themagnetic field intensity axially directed through the cylindrical spacein which the electrons move is of a proper magnitude so that the averageangular velocity of the electrons in the inter-electrode space betweencathode and anode is at or below the value required for the magnetron tofunction as an oscillator. When the signal to be amplified is suppliedto the magnetron, the electric field in the inter-electrode space isincreased to such a value that the magnetron delivers power to the load.The reason why the power delivered to the load is greater than the highfrequency power supplied to the magnetron has been discussed in thepreceding paragraphs. From the explanation therein contained, andparticularly from a consideration of the linearity of the curve of Fig.2, it is readily apparent that as the magnitude of the signal to beamplified is increased the power supplied to the load is proportionatelyincreased.

In the discussion of Fig. 3, there has been described the manner inwhich a conventional magnetron oscillator may be adapted structurallyand the operating parameters may be adjusted so thatthe high power andhigh efiiciency capabilities of magnetron type apparatus may be readilyutilized for amplifying purposes. In such apparatus, the magnetron iscompletely controlled by the external source of electromagnetic energyto be amplified. With apparatus of this kind power gains of from 2 to 10and output powers up to 1000 watts in the frequency range of 500 to 1000megacycles have been obtained. These amplifiers operated with anodeefiiciencies ranging from" 40 to depending upon the kind of magnetrondischarge device used. It should be noted that since the input power tothe magnetron amplifier is also applied to the load, and not lost, theover-all efficiencies are even higher than the above figures indicate.

Referring now to Fig. 4 wherein like numerals designate previouslydescribed parts, there is shown another embodiment of apparatus usefulin carrying out applicants invention. The right-hand section of theapparatus is similar to the magnetron amplifier of Fig. 3 and performsthe amplifying function. The left-hand section is utilized as a sourceof signal to be amplified, that is, as an oscillator. Coupling betweenthe oscillator section and the amplifier section is achieved by meansofa common resonant line 7 short circuited at its ends by members 8 and19, respectively. At the left end of the resonant line is formed theoscillator section and at the other end of the resonant line is formedthe amplifier section. A load 10 similar to the load of Fig. 3 isconnected intermediate the magnetron sections. A tuning sectioncomprising a transmission line 20 and an adjustable tuner 21 connectedto the resonant system at the point on transmission line 7 to which theload is connected is used for tuning the system to the frequency ofoperation. A battery 22 supplies heater power to the cathode of theoscillator section of the magnetron. A battery 23 supplies a voltagebetween anodes 11a, 12a and the cathode 13a of oscillator magnetronsufiicient to cause it to oscillate. The unidirectional magnetic fieldof the oscillator section of the apparatus may be supplied by anysuitable means, such as a coil 24 through which a unidirectional currentis adapted to flow or by means of a permanent magnet. The magnitude ofthe unidirectional anode voltage, the magnitude of the magnetic field,and the resonant frequency of the resonant system are mutuallyinterrelated and are so adjusted that oscillations are developed by theoscillator section of the system. The amplifier section of thisapparatus is adjusted in a manner similar to the apparatus of Fig. 3. Ifidentical magnetrons are used for the oscillator and amplifier sectionsa power gain of two is obtained and as the magnitude of the powerdeveloped by the oscillator increases the power supplied to the loadincreases proportionately due to the contribution of the amplifiersection.

Referring now to Figs. 5a and 5 b of the drawing, there is shown amagnetron device of the kind schematically shown in the systems of Figs.3 and 4. It will be understood that in general our invention isapplicable to all types of traveling wave magnetrons and particularkinds of traveling wave magnetrons are shown in this specification onlyby way of example. The magnetron device of Figs. 5a and 51) includes anenvelope 25 formed of glass, within which is mounted a generallyU-shaped conductor 26 which may to advantage be formed of copper tubing.The arms of the U-shaped tubing extend through the end wall of theenvelope and are sealed thereto by suitable seal constructions includingsleeves 27 and 28 which are joined, respectively, to the envelope andthe arms of the U-shaped conductor and which may be made of any of aclass of conventional compositions suitable for metal to glass sealingand comprising the elements of iron, nickel, and cobalt. The conductor26 includes portions 29 and 30 which extend to the exterior of theenvelope to provide a parallel wire transmission line corresponding tothe parallel wire transmission line 7 of Figs. 3 and 4. Within the tubeenvelope a pair of anode members 30 and 31 corresponding to anodemembers 11 and 12 of Figs, 3 and 4, are supported in opposed relationfrom the opposite arms of U-shaped conductor 26. The anode members arespaced at the inner ends thereof and provided with arcuate surfaces 32and 33 respectively, which cooperate to confine the space charge of thedevice supplied by an elongated cathode 34. The cathode 34, which may bea tungsten wire, is supported on the aXis of the generally cylindricalspace defined by the curved face portions 32 and 33 of the'anodesegments by resilient supporting conductors 35 and 36. These supportingconductors are secured to relatively rigid lead-in conductors 37 and 33respectively, which are, in turn, sealed through the end wall of theenvelope in any suitable manner. Circular shielding members 39 and 40are supported respectively, from the flexible conductors 35 and 36 onopposite sides of the anode structure to prevent electrons escaping fromthe interelectrode space from impinging on the glass walls of theenvelope. Also, a shield member 41 may be connected to the anode member30 and extend over the gap 42 to collect electrons escaping therefrom. Asuitable getter 43 is supported near the inner Wall of the envelope by aconductor 44 secured to the end of the loop conductor 26. While we haveshown and described particular embodiments of our invention, it will beobvious to those skilled in the art that various changes andmodifications may be made without departing from our invention in itsbroader aspects and, we, therefore, aim in the appended claim to coverall such changes and modifications as fall within the true spirit andscope of our invention.

- What we claim as new and desire to secure by Letters Patent of theUnited States is:

A magnetron amplifier comprising a cathode, an anode including an arrayof spaced anode segments defining interaction gaps facing said cathodeand spaced to sustain an oscillation at a traveling wave mode frequency,an output system coupled to said anode segments for sustaining anelectromagnetic wave at said frequency traveling along the array, meansfor introducing an electron space charge between said cathode and saidanode, means for establishing a static electric field between said anodesegments and said cathode and means for establishing an applied staticmagnetic field perpendicular thereto, the ratio of the static electricfield to the static magnetic field determining the average velocity ofsaid space charge along said anode array, means coupling a source ofhigh frequency signals to said output system to modify the electricfield between said cathode and anode to cause high frequency energy tobe generated through traveling wave mode operation by the electron spacecharge at the interaction gaps in excess of the .cou:- pled highfrequency signals, said excess energy being obtained from said staticelectric field, and means for coupling said output system to a load.

References Cited in the file of this patent UNITED STATES PATENTS2,087,737 Runge July 20, 1937 2,184,556 Linder Dec. 26, 1939 2,233,482Linder Mar. 4, 1941 2,278,210 Morton Mar. 31, 1942 2,462,698 Wilbur Feb.22, 1949 2,490,007 Peters Nov. 29, 1949 2,511,407 Kleen et al. June 13,1950 2,528,241 Peters et al. Oct. 31, 1950 2,546,033 Knight Mar. 20,1951 2,562,738 Ramo July 31, 1951 2,576,599 Hansel] Nov. 27,

